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Re: Tyrannotitan, new carcharodontosaurid from Argentina



Tim Donovan (uwrk2@yahoo.com) wrote:

<IIRC teeth similar to those of Acrocanthosaurus were found in an Ethiopian
unit of about the same age but this carcharodontosaurid seems more related to
Giganotosaurus.>

  Teeth in *Acrocanthosaurus* are without wrinkles on the crown at all,
according to Carpenter and Currie. They are more similar to *Allosaurus*. This
(and the absence of a distinct "chin" in the mesial dentary) are more similar
to non-carcharodontosaurs than to them -- not surprising given that recent
phylogenies uphold the relationship of *Acrocanthosaurus* and *Allosaurus*
exclusive of either *Carcharodontosaurus* or *Yangchuanosaurus*. That said, a
dentary for *Carcharodontosaurus* is unknown as yet, so the presence of the
"chin" is not indicative of *Giganotosaurus*-only relationships. Teeth bearing
"wrinkles" are known from the Aptian beds that Rich and Novas previosuly
reported years back, and from Japan and Brasíl, but are absent in North
American beds so far. Teeth from England appear to exhibit banding across the
crown as in *"Megalosaurus" hesperis*, but this may be an artifact of
coloration of the enamel surface, rather than surface texture.

  It;s easy to assume a rather weak phylogeographical transition with Gondwanan
endemism and EK migration into Europe from Africa, then spreading to Asia
either directly (unlikely) or via North America, at which point access to Japan
becomes feasible. This may correspond to *Acrocanthosaurus*, if only it were a
more derived carcharodontosaur than the Patagonian-African taxa, which it seems
is not in keeping with the phylogeny present to hypothesize otherwise (which
would imply migration INTO Gondwana).

<Questionable. GSP wrote that Spinosaurus, despite its large size, would have
been vulnerable to attack by the large allosaurids that shared its African
environment.>

  Lions are vulnerable to hyenas and leopards, but remain key predators.
Spinosaurids are claimed to be vulnerable to carchs, but 1) *Spinosaurus*
probably massed more than *Carcharodontosaurus,* which would have been slender,
narrow and gracile, as in other allosauroids, whereas the
"megalosaur/spinosaur" groups are distinctly robust and broad, and the ribcage
in the Egyptian "fisheater" was extremely broad. 2) There is no such thing as a
HUGE exclusive piscivore, and all large piscivores today (including whales,
sharks and gharials, relative to their ecologies) take non-piscine prey
frequyently enough to be considered opportunistic. 3) The snout of spinosaurs
also appears to lack many piscivore traits including a rounded cross-section,
but is mediolaterally narrow with deep roots, indicating a strong adaptation to
vertical compressive forces, such that spinosaurs likely had a VERY powerful
bite, as opposed to a weak bite in, say, *Allosaurus*. So, gives points 1, 2
and 3, it is more likely that the jaw and body variation cleanly separated
spinosaurs from carchs in both prey choices and ecology, and if anyhing, in a
fight, I'd bet on spinosaurs to come out kicking and winning.

<Lamanna mentioned a Campanian carcharodontosaurid and suggested that the
Maastrichtian Abelisaurus might be one.>

  Some ideas need to wait for publication before being used to counter
arguments. We should use published, verifiable data first.

  Cheers,

Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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